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EOS 4.36.1F User Manual - Monitoring Latency 打印

Monitoring Latency

The Monitoring Latency feature allows the measurement and display of end-to-end packet latency as seen at egress interfaces. EOS measures packet latency from switch ingress to switch egress and provides two modes of operation:
  • Maximum Load - Record and display the maximum end-to-end latency experienced by any packet egressing from the switch at each egress interface and traffic class.
  • Histogram - For each egress interface and traffic class combination, record and display a histogram of up to 4 bins counting packets. Configure the bin boundaries to your custom parameters, and packets with a latency between the lower and upper boundaries for a bin count in that bin.
Note: Supported on the 7280R3A, 7289R3A, and 7800R3A series of platforms.

Monitoring Latency Configuration

Use the following command to enter the Monitor Latency Configuration Mode:

switch(config)# monitor latency
switch(config-mon-latency)#

Use the following command to enable maximum mode and begin recording latency data for the mode:

switch(config-mon-latency)# measurement end-to-end maximum
switch(config-mon-latency)#

Use the following command to enable histogram mode and begin recording latency data for the mode:

switch(config-mon-latency)# measurement end-to-end histogram
switch(config-mon-latency)#

The maximum and histogram modes can be enabled together in a single command.

switch(config-mon-latency)# measurement end-to-end histogram maximum
switch(config-mon-latency)#

The [no | default] versions of the command disables the feature.

Configuring Histogram Bin Boundaries for a Profile

The End-to-End Binning Profile defines a set of increasing boundary values that groups latency values into a histogram with up to 4 bins. Specify up to 5 boundary values, in milliseconds, microseconds, or nanoseconds, for the 4 bins. You must configure explicit minimum and maximum boundary values of zero and infinity. Packets experiencing latency with a value between the lower and upper boundaries count for that bin.

The following restrictions apply to the configuration of a binning profile:

  • Boundaries must be specified in increasing order.
  • Specify at least 2 bins with 3 values: 0, boundary value, and infinity.
  • EOS supports up to 4 bins with boundary values of 0 and infinity plus 3 other boundary values.
  • In the switch hardware, the binning boundary values consist of 32-bit values specifying nanoseconds even if specified as milliseconds, microseconds, or nanoseconds. The maximum configurable value is approximately 4.29 seconds.
  • EOS does not support boundary values using sub-nanosecond precision. If specifying a boundary with sub-nanosecond precision, EOS truncates the nanosecond portion of the value and uses the truncated value as the boundary value.

Changing the binning profile clears existing histogram data and the message, "Changing histogram boundaries clears the histogram counters."

If you do not specify a binning profile, the configuration uses a default profile:

binning profile end-to-end microseconds 0 10 50000 infinity

Example Profiles

switch(config-mon-latency)#binning profile end-to-end milliseconds 0 0.01 0.2 50.3 infinity
switch(config-mon-latency)#binning profile end-to-end microseconds 0 10 200 50300 infinity
switch(config-mon-latency)#binning profile end-to-end nanoseconds 0 10000 200000 50300000 infinity

Use the clear command to clear recorded latency data and restart updating it.

Displaying the Latency Data Histogram

The output of the show monitor latency measurement end-to-end histogram displays the following information:

  • Latency(nanoseconds) - For each histogram bin, it displays the range of packet latencies assigned to the bin.
  • Count - The number of packets experiencing latency in this range since clearing the last count.
  • Cumulative% - The cumulative percentage of total packets received on the interface and traffic class combination accounted for by the row and previous rows.
  • Histogram - The count value displayed as a string of "*" characters with a maximum of 20 characters.
switch# show monitor latency measurement end-to-end histogram
Interface: Ethernet3/2/1
Traffic class: 0
Latency histogram:
Latency (nanoseconds)       Count       Cumulative %    Histogram            
--------------------------- ----------- ------------------ ---------------------
           0 -  9999        1234               23.1    |**********          
       10000 - 19999        2468               69.3    |********************
       20000 - 29999         702               82.5    |******              
       30000+                936              100.0    |******** 
   
Interface: Ethernet3/2/1
Traffic class: 1
Latency histogram:
Latency (nanoseconds)       Count       Cumulative %    Histogram            
--------------------------- ----------- ------------------ ---------------------
           0 -  9999        1234               23.1    |**********          
       10000 - 19999        2468               69.3    |********************
       20000 - 29999         702               82.5    |******               
       30000+                936              100.0    |********

Displaying the Latency Data Maximum Mode Information

The output of the show monitor latency measurement end-to-end maximum displays the following information:

  • Interface - Displays the interface configured for maximum mode.
  • TC - Displays the traffic class with the maximum value.
  • Maximum Latency(nanoseconds) - The largest latency experienced by any packet egressing the switch from the indicated interface and traffic class since clearing the last maximum values.
  • Last seen - Displays the time when the maximum value was last seen.
switch# show monitor latency measurement end-to-end maximum
                            Maximum latency               
Interface           TC         (nanoseconds)    Last seen  
---------------- -------- --------------------- -----------
Ethernet2            0                 10000    0:00:02 ago
Ethernet2            7                  3000    0:01:12 ago
Ethernet13           0                 10000    0:00:02 ago
Ethernet13           7                  3000    0:01:12 ago
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